The present invention relates generally to fiber optic connectors, and more particularly, to a fiber optic connector including a multifiber ferrule and means for applying an axial biasing force to the ferrule.
The proliferation of optical communications and data transfer has dramatically increased the use of fiber optic connectors including multifiber ferrules for simultaneously interconnecting a plurality of optical fibers. Not only are multifiber connectors being utilized in greater numbers, but increased performance demands are being placed upon the optical connections between mated connectors. As a result, there is an increased demand in optical communications for what has become generally known as “low-loss, intermateable, multifiber connectors.” For example, in order to maximize signal transmission between pairs of opposed optical fibers, multifiber connectors are required to align each of the optical fibers very precisely, especially for single mode applications. In this regard, multifiber connectors are typically required to align each optical fiber to within about 7 to 14 microns for multimode applications and to within about 0 to 3 microns for single mode applications.
In order to provide the desired alignment, conventional multifiber ferrules define a pair of elongate alignment holes that receive and cooperate with respective alignment members, such as guide pins, to accurately align opposing ferrules, and in turn, the optical fibers mounted within the multifiber ferrules. For example, one conventional type of multifiber ferrule is the MT (Mechanically Transferable) ferrule, such as described by U.S. Pat. No. 5,214,830 to Sinji Nagasawa, et al., and assigned to Nippon Telephone and Telegraph Corporation of Tokyo, Japan. The MT ferrule has a generally rectangular shape in lateral cross-section and defines a pair of guide pin holes and a plurality of optical fiber bores opening through the end face of the ferrule. The guide pin holes receive respective guide pins to align the optical fibers of a pair of opposing MT ferrules.
The pair of MT ferrules that are to be interconnected are typically configured such that one of the multifiber connectors has a male configuration and the other multifiber connector has a female configuration. The male configuration of the multifiber connector includes a pair of guide pins that have been inserted within the guide pin holes defined by the MT ferrule and extend forwardly beyond the end face. In contrast, the female configuration of the multifiber connector includes an MT ferrule that defines a pair of guide pin holes for receiving the portions of the guide pins that extend beyond the end face of the male MT ferrule. During mating, insertion of the guide pins into the guide pin holes defined by the female MT ferrule aligns the male and female connectors, and in turn, aligns the optical fibers mounted within the MT ferrules. In order to snugly receive the guide pins, the guide pin holes defined by a conventional MT ferrule are cylindrical in lateral cross-section so as to have the same size and shape along their entire length. By utilizing cylindrical guide pin holes, the sidewalls of the guide pin holes contact the guide pins along their entire length, thereby maximizing the alignment provided by the guide pins.
The MT ferrules of the male and female fiber optic connectors are biased towards one another so as to interconnect the optical fibers with a minimum amount of attenuation. It has long been believed that “dry physical contact” (i.e., physical contact between opposing optical fibers without the use of index-matching gel) across all of the pairs of optical fibers of mated multifiber connectors could be achieved by controlling the geometry of the opposing optical fibers and ferrules. However, significant advances in geometry control, such as optimal fiber height, array uniformity, optical fiber angle, core dip and ferrule end face angle, have not consistently resulted in dry physical contact across all of the optical fibers of opposing multifiber connector pairs. Further analysis of the factors preventing dry physical contact of the optical fibers has shown that the force applied to bias the ferrule in the axial direction of the mating ferrule very often produces a moment about a lateral axis of the ferrule. In other words, the biasing force is not always applied along the longitudinal axis of the ferrule, or at the least, is not balanced about the longitudinal axis of the ferrule.
Typically, the biasing force is generated by a coil spring mounted within a connector housing between the rear face of the ferrule and a spring push. An off-axis biasing force oftentimes results because the coil spring buckles within the connector housing and introduces a component of the spring force that is offset from the longitudinal axis of the ferrule, or is applied at an angle other than normal to the end face of the ferrule. Even if the coil spring does not buckle, the geometry and inherent nature of the coil spring makes it likely that an unbalanced biasing force will be applied to the rear face of the ferrule in a direction other than along the longitudinal axis. As a result, the biasing force will apply an undesired moment to the ferrule in addition to the desired axial force. Thus, despite the presence of substantially perfect geometry features in mating optical fibers and ferrules, a biasing force that is not applied along the longitudinal axis of a multifiber ferrule, or is not balanced about the longitudinal axis of a multifiber ferrule, will not consistently produce dry physical contact between a mated pair of fiber optic connectors.